Light responsive system



P 23, 8 J. F. HOWELL 2,853,652

LIGHT RESPONSIVE SYSTEM 2 Sheets-Sheet 1 Filed Oct. 12. 1953 INVENTORF- JOHN F HOWELL BY.'-- W11 9. @0(,t

ATTORNEY Sept. 23, 1958 J. F. HOWELL LIGHT RESPONSIVE SYSTEM 2 Sheets-Sheet 2 Filed Oct. 12, 1953 INVENTOR.'-- LOHN F. HOWELL ATTORNEY United States Patent LIGHT RESPONSIVE SYSTEM John F. Howell, Milwaukee, Wis., assignor to General Electric Company, a corporation of New York Application October 12, 1953, Serial No. 385,481

19 Claims. (Cl. 315-83) The present invention relates in general to illumination and has more particular reference to the control of light emitting lamps, especially vehicle headlights, the invention pertaining specifically to an improved system operable automatically to dim the headlights of a vehicle in response to the head-on approach of another headlighted vehicle.

Vehicle headlights commonly comprise electric lamps containing dual filaments in combination with reflector means, the filaments being positioned with respect to the associated reflector means so as to project a so-called high or bright light beam substantially horizontally when one of the filaments is energized, a downwardly inclined so-called low or dim light beam being emitted when the other of said filaments is energized. The bright light beam is usually employed for normal night driving purposes, it being the practice to dim the headlight by extinguishing the bright light beam and energizing the dim light beam filament when approaching another vehicle traveling in the opposite direction, at night, in order to eliminate driving hazards due to the eyedazzling effect of the high beam upon the operator of the approaching vehicle.

For headlight dimming purposes it is conventional to provide a dimming switch operable, as by foot pressure of the vehicle operator, to disable the bright light beam filament while energizing the dim beam filament.

An important object of the present invention is to provide automatic control means operable to dim the headlights of a vehicle in response to the approach of another lighted vehicle proceeding in the opposite direction and to restore the vehicle headlights to bright condition immediately after the approaching vehicle shall have passed by; a further object being to provide automatic headlight control equipment of simple yet rugged character, adapted to furnish trouble-free operation during an extensive service life; a further object being to provide equipment of the character mentioned adapted for easy installation and interconnection with existing headlight energizing circuits.

Another important object is to provide an improved photosensitive control system embodying a light detecting element comprising a semi-conductor material and electrical translation means controlled by the detector element and operable in response to variations in the impedance thereof to actuate a relay switch for headlight dimming purposes.

Another important object is to provide a system of the character mentioned utilizing, as a sensitive light detector, an element comprising crystalline semi-conductor material from the class including cadmium sulphide, mercury sulphide and cadmium selenide, the same comprising electron donor semi-conductors.

Another important object is to provide a control system of the sort mentioned, wherein the response of the light sensitive detector is employed to correspondingly affect a phase sensitive relay circuit for the selective operation of light dimming means; a further object being 2,853,652 Patented Sept. 23, 1958 to operate a lamp dimming relay switch by means of an electron fiow valve controlled in accordance with the phase condition of cyclically pulsating actuating energy applied on the valve, including means for altering the phase condition of such valve applied energy as a function of detector response.

Another object is to provide a control system of the sort mentioned including a light sensitive detector and having a lamp dimming relay switch actuating valve, in cluding anode, cathode and grid, means to render the valve conductive to operate the relay switch to one position when the detector is dark, means operable to render said valve non-conductive to operate said switch to another position in response to illumination of the detector at above a selected intensity, and an over-riding switch operable to connect the cathode and grid of the valve to render the same conductive at will while the detector is illustrated at above the selected intensity.

Another important object is to operate the detector by applying thereto cyclically pulsating electrical power at relatively elevated potential derived from a relatively low voltage uni-directional power source.

The foregoing and numerous other important objects and inherent functions of the invention will become apparent as the same is more fully understood from the following description which, taken in conjunction with the accompanying drawings, discloses a preferred embodiment of the invention.

Referring to the drawings:

Figs. 1 and 2 are diagrammatic showings illustrating the head-on approach of headlighted vehicles;

Fig. 3 is a diagrammatic representation of a light responsive control system embodying the present invention; and

Fig. 4 is a sectional view through a light sensitive de tector device employed in the system shown in Fig. 3.

To illustrate the invention the drawings show a vehicle V carrying a pair of vehicle headlamps L' for projecting beams of light R outwardly of the vehicle in which the lamps are mounted. Each of the lamps L' may embody a high or bright beam filament 12 and a low or dim beam filament 13, one end of each of said filaments being electrically connected to the preferably grounded side of a suitable electrical power source 14. The ground remote ends of the high beam filaments may be electrically interconnected with one contact 15H of a single pole, double throw dimmer switch 15. The ground remote ends of the low beam filaments may also be interconnected with another contact 15L of said dimmer switch, the pole of the dimmer switch being electrically connected with the ground remote side of the power source 14, as through suitable circuit devices which may include disconnecting switch means, a fuse, other circuit devices, including a meter, if desired, one or more choke coils 17 connected in series, and condensers 18 each connected between the grounded side of the power source and the source remote end of a corresponding choke coil.

The power source 14 may conveniently comprise a conventional storage battery of the sort commonly provided as standard equipment in automotive vehicles for the operation of headlights and other electrical equip ment. When the pole of the switch 15 is connected with the power source 14 it will be seen that the bright and dim beam filaments 12 and 13 may be alternately energized by operation of the dimmer switch 15, as by selectively energizing the operating coil 15C thereof. To this end, the switch 15 may be biased to normally close the blade with the contact element 15H, the blade being movable in response to excitation of the coil 15C to disengage the contact 15H and to make contact with the element 15L.

In order to provide for the automatic control of the headlights L in response to the head-on approach of another headlighted vehicle, such as the vehicle V the present invention contemplates a light responsive, electrically actuated translation system 20 adapted to energize the relay coil C in response to the head-on approach of said other headlighted vehicle V when the intensity of headlight beams R which reach the vehicle V from the headlamps L of the approaching vehicle V attains a selected lamp dimming level. To this end, the system 21) may comprise a light sensitive detector 21 mounted in position to receive the impingement of light rays R emitted by the headlights of the approaching vehicle, said detector 21 preferably comprising a semi-conductor material of the electron donor type, particularly crystalline material selected from the class comprising cadmium sulphide, mercury sulphide, and cadmium selenide. These crystalline semi-conductors exhibit the power of altering the impedance of their constituent material as a function of the intensity of light rays impinging thereon. The detector 21, accordingly, may be made to control the system to energize the coil 15C when the impedance of the detector reaches a predetermined value in response to increasing intensity of the headlight beams R of the approaching vehicle.

The light sensitive crystal detector 21 is preferably sealed within a translucent preferably glass envelope E, which may either be evacuated or else charged with a preferably inert gas, such as nitrogen. The envelope E may comprise a cylindrical member formed with an integral, preferably herni-spherical closure wall at one end of the cylindrical member. The crystal detector 21 may be electrically connected on and between the ends of a pair of spaced apart, electrically conducting support stems S mounted substantially parallel within the cylindrical member in position supporting the detector 21 substantially at and within the hemi-spherical end closure wall of the envelope E. The stems S preferably comprise metal members capable of being sealed to glass, and said stems, remote from the detector 21, may form glass-to-metal seals with a stem supporting end closure wall sealing said envelope at the end thereof remote from said hemi-spherical closure wall. The detector mounting stems may extend through and outwardly of said stem supporting end closure wall for connection with the translation system 28. If desired, the stern supporting end closure wall may also be formed with sealable duct means D through which the envelope may be evacuated and charged with inert gas.

The detector enclosing envelope may be mounted in position presenting the detector crystal 21 at the focus of a light collecting reflector device C, which may conveniently comprise a parabolic shell formed with internal light reflecting mirror surfaces adapted to deliver, at the focus of the device, all light rays entering the open end of the shell. The shell at its apexial portion, opposite the open end thereof, may be fitted with a mounting sleeve M sized to snugly yet slidingly receive the cylindrical envelope E; and said envelope may be secured. and anchored in the sleeve, in position presenting the crystal 21 at the focus of the light collecting device, as by means of any suitable preferably quick drying cement, such as malachite basic cement.

Energy from the relatively low voltage uni-directional power source 14 may be applied through a vibrator device 22 to the primary winding 23 of a transformer 24, said primary winding 23 having a center tap connected preferably with the high or ground remote side of the power source 14, as through the choke coils 17, the opposite ends of the winding 23 being respectively connected with a stationary contact of the vibrator device, the pole of which is connected with the grounded side of the power source.

The transformer 24 embodies a secondary winding 25, having a grounded center tap and opposite ends connected to supply electrical power of cyclically pulsating character and relatively high voltage for the operation of the system 20 under the control of the detector 21. A condenser 25' may be connected across the secondary transformer winding 25, if desired. The system 20 may comprise a pair of electron flow valves 26 and 26, each having an anode 27, 27, a cathode 28, 28, and a control grid 29, 29'. The anode 27 of the valve 26 may be electrically connected with one end 25 of the transformer winding 25, the cathode 28 of said valve 26 being connected to the opposite end 25 of the winding 25, to ground and to the control grid 29' of the other valve 26, respectively through resistors 30, 31 and 32. The cathode of the valve 26 may be connected directly to ground and its anode may be connected to the same ground remote end of the transformer winding 25 to which the anode of the valve 26 is connected, to thereby form a relay switch operating circuit for controlling the operation of the lamps L. The said switch operating circuit preferably comprises the actuating coil 33C of a single pole, double throw relay switch 33 comprising stationary contact elements 33H and 33L and a blade normally urged into engagement with the element 33L when the coil 33C is not excited. When the coil 33C is energized, the blade of the switch 33 will be in position engaged with the element 33H and released from the element 33L. If desired, a condenser 34 may be connected between the opposite ends of the coil 33C.

The cathodes 28 and 28' of the valves 26 and 26 may of course be excited by filaments energized by the power source 14. The grid 29 of the valve 26 may be interconnected with the transformer winding 25 by means of relatively parallel circuits 35 and 35'. The circuit 35 connects said grid 29, through the detector 21, with the end 25 of the transformer winding 25 remote from the end 25 thereof that is connected with the plate or anode of the valve 26. The circuit 35, on the other hand, connects the grid 29 with the end 25 of the transformer winding which is connected with the plate or anode 27 of the valve 26, such connection being accomplished through a pair of resistors 36 and 36, a potentiometer 37, and a resistor 38, one end of the potentiometer being connected with the ungrounded or high side of the power source and its other end being connected through the resistor 38 with the side 25 of the transformer winding 25. The interconnected ends of the resistors 36 and 36' also may be connected in an offset circuit through a potentiometer 39 with the contact element 33L of the relay switch.

The blade of the relay switch 33 may be connected with the high side of the power source 14. The switch contact element 33H may be connected to the low or grounded side of the power source 14 through the switch actuating coil 15C.

The potential developed in the transformer winding 25 between the grounded center tap thereof and either end will at all times be out of phase with respect to the potential developed between the grounded center tap and the opposite end of the winding. Accordingly, the potential applied upon the grid 29 of the valve 26, through the detector 21, will always be 180 out of phase with respect to potential applied on the grid through the resistors 36, 36 and 38 and the potentiometer 37. When the detector is dark, its impedance is very high so that the circuit 35 is substantially blocked at the detector element 21.

As a consequence, the potential on the grid will predominantly comprise that supplied between the grounded center tap and the end 25' of the transformer winding 25. Since this is in phase with the voltage that is applied to the plates 27 and 27' of the valves 26 and 26', the same will be rendered conducting when the detector is dark, the valve 26 serving as a cathode follower or isolation stage to reduce the capacity associated with the input circuit of the valve 26'. The valve 26 when in conducting condition, of course, applies the voltage developed in the transformer winding between the center tap and end 25 thereof upon the grid of the valve 26', through the resistor 32. The valve 26', accordingly, is in conducting condition whenever the valve 26 is also in conducting condition, that is to say, when the detector is dark.

So long as the valve 26 is in conducting condition, the switch actuating coil 330 will be energized to hold the switch blade closed against the contact element 33H and open with respect to the contact element 33L. The energizing circuit of the switch actuating coil C will accordingly be closed and the blade of the switch 15 consequently held in closed position against the contact element 15H thereof, which is connected with the high beam lamp filaments 12. The lamps L, accordingly, will emit a high or bright beam so long as the detector 21 remains dark.

When the light beam R of an approaching vehicle V impinges upon the detector 21, the impedance thereof will decrease as a proportional function of the intensity of the impinging light. The decrease in impedance allows progressively larger amounts of potential to be applied upon the grid 29 of the valve 26, from between the center tap and the end 25 of the transformer winding. When the intensity of detector impinging light reaches a value determined by the adjustment of the potentiometer 37, the valve 26 and consequently also the valve 26 will become non-conducting, thus allowing the switches 15 and 33 to disconnect the blades thereof from the contact elements 15H and 33H, by discontinuing the supply of actuating energy to the relay switch coils 15C and 33C. The high or bright beam filaments of the lamps L will consequently be extinguished, and the low or dim filaments will become energized as the result of the disengagement of the blade of the switch 33 from the contact element 33H, and the consequent disablement of the switch operating coil 15C which allows the blade of the switch 15 to engage with the contact element 15L, while releasing said blade from the element 15H. The valve 26 thus operates as a phase sensitive switch controlled by the detector 21 for the operation of the light dimming mechanism.

When the lamps L are in low beam operation, the blade of the switch 33 will be in engagement with the contact element 33L and so connect the interconnected ends of the resistors 36 and 36' with the ground remote side of the power source, through the offset potentiometer 39, thereby changing the level of potential supplied to the grid 29 from the transformer winding 25, through the potentiometer 37, in desired fashion.

During the short interval while the valves warm up after being first placed in operation, the relay coil 33C Will not be energized. The lamps L' accordingly will be held in dimmed condition with switch 33L closed and switch 33H open. In order to allow dimmed lights to be brought to bright condition while the detector 21 is illuminated at light dimming intensity, a switch 40 may be provided for connecting the grid 29' of the valve 26 With the cathode 28 thereof, thereby rendering the valve conductive regardless of the condition of the valve 26. Theswitch 40 thus comprises an over-riding switch allowing the coil 33C to be energized in order to thus operate the switches 33 and 15 to energize the bright beam filaments 12 of the lamps L, in the event that the on-coming vehicle V fails to dim its lamps L in response to the dimming of the lamps L.

The function of the offset circuit comprising the potentiometer is, of course, to obviate the possibility of returning the dimmed lamps L to bright beam operation as the result of the dimming of the lamps of the approaching vehicle.

It is thought that the invention and its numerous attendant advantages will be fully understood from the foregoing description, and it is obvious that numerous changes may be made in the form, construction and arrangement of the several parts without departing from the spirit or scope of the invention, or sacrificing any of its attendant advantages, the form herein disclosed being a preferred embodiment for the purpose of illustrating the invention.

The invention is hereby claimed as follows:

1. The method of controlling an electron flow valve in response to impedance variations in a valve monitoring element which comprises applying a cyclically fluctuating valve control potential wave upon the grid of the valve and simultaneously applying, on the grid of said valve, a bucking potential wave of fluctuating character and displaced as to phase 180 with respect to said valve control potential wave, varying the intensity of said bucking potential wave in accordance with the impedance of said monitor element, and then changing the potential level of the control wave after the intensity of the bucking potential wave reaches a pre-determined value.

2. The method of operating a translation system embodying an electron flow valve in response to light induced impedance fluctuations in a light sensitive detector element, which comprises the production of cyclically fluctuating voltage waves of opposite polarity, applying one of said waves, as a control wave, upon the control grid of the valve through a ballasting reactance while applying the other of said waves through said detector element, as a bucking wave, whereby the valve may be operated in response to the diiferential of the waves as a function of the light sensitive response of said detector element, when the potential of the bucking wave reaches a selected value, and then changing the potential level of the control wave after the intensity of the bucking potential wave reaches a selected value.

3. The method of operating a translation system embodying an electron flow valve in response to light induced impedance fluctuations in alight sensitive detector element, which comprises normally applying a bias at a selected voltage level to the control grid of the valve, to determine the response sensitivity and conductive condition of the valve, while applying cyclically fluctuating voltage waves of opposite polarity, upon the control grid of the valve, respectively through a ballasting resistance and through said detector element, whereby the conductive condition of the valve may be changed in response to the differential of said waves, as a function of the light sensitive response of said detector element, and altering the bias applied on the control grid to obtain a different response sensitivity of the valve after its conductive condition becomes changed.

4. Control apparatus comprising an electrical power operated device, a photosensitive detector having variable impedance characteristics, electron flow valve means for controlling the operation of said device, means to apply a cyclically fluctuating electrical potential wave upon.

said valve means to normally condition the same for operation, means controlled by said detector in accordance with the variable impedance thereof for applying on the valve means a bucking potential wave of potential varying with the impedance of the detector, said bucking potential being of fluctuating character like and displaced as to phase with respect to said electrical potential wave, and offset means operable to alter the potential level of said electrical potential wave when the potential of the bucking wave reaches a selected value.

5. Control apparatus as set forth in claim 4, wherein the photosensitive detector comprises crystalline semiconductor material of the electron donor type selected from the class comprising the selenide and sulphide of cadmium and the sulphide of mercury.

6. Control apparatus comprising an electrical power operated device, a photosensitive detector having variable impedance characteristics, electron flow valve means for controlling the operation of said device, means to produce cyclically fluctuating potential waves of opposite polarity, means to apply one of said waves as a valve conditioning wave on said valve to condition the same for operation, means to apply the other wave on said valve under the control of said detector to buck the valve conditioning effect of said valve conditioning wave as a function of light induced variation in the impedance of the detector, to thereby disable the valve when the intensity of light impinging on the detector reaches a selected level, and offset means operable to alter the potential of said valve conditioning wave when the valve becomes disabled.

7. Control apparatus comprising an electrical power operated device, a photosensitive detector having variable impedance characteristics, electron flow valve means for controlling the operation of said device, means to apply a bias upon said valve means at a selected potential level, to determine the response sensitivity of said valve means, means for applying a cyclically fluctuating electrical potential wave upon said valve means to normally condition the same for operation, means controlled by said detector in accordance with the variable impedance thereof for applying on the valve means a bucking potential wave of potential varying with the impedance of said detector, said bucking potential being of fluctuating character like and displaced as to phase with respect to said electrical potential wave to thereby disable the valve means when the potential of the bucking wave reaches a selected level, and means for altering said bias to correspondingly change the response sensitivity of said valve means while the same remains in disabled condition.

8. Control apparatus comprising an electrical power operated device, a photosensitive detector having variable impedance characteristics, electron flow valve means for controlling the operation of said device, means to produce cyclically fluctuating potential waves of opposite polarity, means including an adjustable resistance for applying in phase components of one of said waves at selected intensity levels respectively on the plate and grid of said valve to cause normal valve operation, and means to apply the other wave, upon the grid of said valve, as a valve disabling wave under the control of said detector.

9. Control apparatus comprising a relay device, a photosensitive semi-conductor forming a light detector having impedance characteristics which vary as a function of the intensity of detector impinging light, electron flow valve means including a valve control element, means for producing cyclically fluctuating potential waves of opposite polarity, means for applying one of said waves on said valve control element as a normal valve conditioning wave to activate said valve to control the operation of said relay device in one direction, and means to apply the other wave on said valve under the control of said detector to progressively offset the valve actuating effect of said normal wave and thereby disable said valve means to cause operation of said relay device in the reverse direction when the intensity of light impinging on the detector reaches a selected level.

10. Control apparatus comprising an electrical power operated device, a photosensitive detector having impedance characteristics which vary as a function of the intensity of detector impinging light, electron flow valve means for controlling the operation of said device, said valve means embodying a control grid, a transformer having a secondary winding formed with a center tap, means to operate said transformer to produce cyclically fluctuating potential waves of alternating character respectively between said center tap and each of the opposite ends of said winding, the wave thus produced between said center tap and one end of the winding being displaced as to phase 180 with respect to the wave produced between the center tap and the opposite end of said winding, means to electrically connect one end of said winding with the grid of said valve means, and means to connect the other'end of said winding with said grid, through said detector, whereby to bias said valve means for operation and to disable the same, to thereby ener- 8 gize and de-energize the power operated device as the intensity of detector impinging light increases above and falls below a selected level.

11. Control apparatus comprising an electrical power operated device, a photosensitive detector having impedance characteristics which vary as a function of the intensity of detector impinging light, electron flow valve means including a control valve for controlling the operation of said device and a switching valve for actuating the control valve, the grid of said control valve being connected with the cathode of the switching valve, a transformer having a secondary winding formed with a center tap, means to operate said transformer to produce cyclically fluctuating potential waves of alternating character displaced as to phase respectively between said center tap and each of the opposite ends of said winding, means to electrically connect one end of said winding with the grid of said switching valve and also with the anodes of both valves, and means to connect the other end of said winding with said grid, through said detector, whereby to normally bias said switching valve for opera tion and to disable the same, to correspondingly actuate and deactivate said control valve and thereby energize and de-energize the power operated device as the intensity of detector impinging light increases above and falls below a selected level.

12. Control apparatus comprising an electrical power operated device, a photosensitive detector having impedance characteristics which vary as a function of the intensity of detector impinging light, electron flow valve means including a device driving valve connected to control the operation of said device, a switching valve for controlling the device driving valve, means operable to produce cyclically fluctuating potential waves of alternating character and displaced as to phase 180, means to apply in phase components of one of said waves, respectively, on the plate of the switching valve and as a valve actuating bias on the grid of said switching valve, and means to apply a component of the other of said waves upon said grid, through said detector, whereby to bias said switching valve for operation and to disable the same, to thereby control the device energizing and de-energizing action of said device driving valve, as the intensity of detector impinging light increases above and falls below a selected level.

13. Control apparatus comprising an electrical power operated device, a photosensitive detector having variable impedance characteristics, electron flow valve means for controlling the operation of said device, means to pro duce cyclically fluctuating potential waves of opposite polarity, means including an adjustable resistance for applying one of said waves at a selected intensity level on said valve as a valve conditioning wave for causing normal valve operation, means to apply the other wave, upon said valve, as a valve disabling wave under the control. of said detector, and an over-riding switch connected to actuate said device regardless of the condition of said valve means.

14. Control apparatus comprising an electrical power operated device, a photosensitive detector having variable impedance characteristics, electron flow valve means including a device driving valve, and a switching valve for controlling operation of the driving valve, means to produce cyclically fluctuating potential waves of opposite polarity, means including an adjustable resistance for applying one of said waves at a selected intensity level on said switching valve as a valve conditioning wave for causing normal valve operation, means to apply the other wave, upon said valve, as a valve disabling wave under the control of said detector, and an ovcr-riding s itr'n connected with said device driving valve and operable to activate the same for the operation of said device regardless of the condition of said switching valve.

15. Control apparatus for automatically dimming vehicle lamps in response to the head-on approach of another vehicle comprising a relay switch device controllingly connected in the vehicle lamp energizing system and selectively operable to cause bright and dim operation of said lamps, a photosensitive detector disposed in position to be illuminated by a light beam emitted by an approaching vehicle, said detector having impedance characteristics which vary as a function of detector impinging light, electron flow valve means for controlling the operation of said device, means to produce cyclically fluctuating potential waves of opposite polarity, means including an adjustable resistance for applying one of said waves at a selected intensity level on said valve as a valve conditioning wave for causing normal valve operation, and means to apply the other wave, upon said valve, as a valve disabling wave under the control of said detector.

16. Control apparatus for automatically dimming vehicle lamps in response to the head-on approach of another vehicle comprising a relay switch device controllingly connected in the vehicle lamp energizing system and selectively operable to cause bright and dim operation of said lamps, a photosensitive detector disposed in position to be illuminated by a light beam emitted by an approaching vehicle, said detector having impedance characteristics which vary as a function of detector impinging light, electron flow valve means including a device driving valve, and a switching valve for controlling operation of the driving valve, means for producing cyclically fluctuating potential waves of opposite polarity, means for applying one of said waves on the control grid of said switching valve as a normal valve conditioning wave to activate said valve to control the operation of said relay device in one direction, and means to apply the other wave on said grid under the control of said detector to progressively offset the valve actuating effect of said normal wave and thereby disable said valve means to cause operation of said relay device in the reverse direction when the intensity of light impinging on the detector reaches a selected level.

17. Control apparatus for automatically dimming vehicle lamps in response to the head-on approach of another vehicle comprising a relay switch device controllingly connected in the vehicle lamp energizing system and selectively operable to cause bright and dim operation of said lamps, a photosensitive detector disposed in position to be illuminated by a light beam emitted by an approaching vehicle, said detector having impedance characteristics which vary as a functionof' detector impinging light, electron flow valve means including a device driving valve, and a switching valve for controlling operation of the driving valve, means to produce cyclically fluctuating potential waves of opposite polarity, means including an adjustable resistance for applying one of said waves at a selected intensity level on said switching valve as a valve conditioning wave for causing normal valve operation, means to apply the other wave, upon said valve, as a valve disabling wave under the control of said detector, and an over-riding switch connected with said device driving valve and operable to activate the same for the operation of said device regardless of the condition of said switching valve.

18. Control apparatus for automatically dimming vehicle lamps in response to the head-on approach of another vehicle comprising a relay switch device controllingly connected in the vehicle lamp energizing system and selectively operable to cause bright and dim operation of said lamps, a photosensitive detector disposed in position to be illuminated by a light beam emitted by an approaching vehicle, said detector having impedance characteristics which vary as a function of detector impinging light, electron flow valve means including a control valve for controlling the operation of said device and a switching valve for actuating the control valve, the grid of said control valve being connected with the cathode of the switching valve, a transformer having a secondary winding formed with a center tap, means to operate said transformer to produce cyclically fluctuating potential waves of alternating character displaced as to phase respectively between said center tap and each of the opposite ends of said winding, means to electrically connect one end of said winding with the grid of said switching valve and also with the anodes of both valves, and means to connect the other end of said winding with said grid, through said detector, whereby to normally bias said switching valve for operation and to disable the same, to correspondingly actuate and deactivate said control valve and thereby energize and deenergize the relay device as the intensity of detector impinging light increases above and falls below a selected level. 1

19. Control apparatus for automatically dimming vehicle lamps in response to the head-on approach of another vehicle comprising a relay switch device control lingly connected in the vehicle lamp energizing system and selectively operable to cause bright and dim operation of said lamps, a photosensitive detector disposed in position to be illuminated by a light beam emitted by an approaching vehicle, said detector having impedance characteristics which vary as a function of detector impinging light, electron flow valve means for controlling the operation of said device, said valve means embodying a control grid, a transformer having a secondary winding formed with a center tap, means to operate said transformer to produce cyclically fluctuating potential waves of alternating character respectively between said center tap and each of the opposite ends of said winding, the wave thus produced between said center tap and one end of the winding being displaced as to phase 180 with respect to the wave produced between the center tap and the opposite end of said winding, means to electrically connect one end of said winding with the grid of said valve means, and means to connect the other end of said Winding with said grid, through said detector, whereby to bias said valve means for operation and to disable the same, to thereby energize and de-energize the relay device as the intensity of detector impinging light increases above and falls below a selected level.

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